Spaceflight stunts hair growth?

As if astronauts on the International Space Station didn’t suffer enough. Alongside muscle and bone wasting, bouts of depression and anxiety and a weaker immune system, a new study shows their hair growth may become sluggish in space too.

Japanese scientists led by Masahiro Terada from Jikei University in Tokyo analysed genes controlling hair growth in astronauts who’ve been in orbit long-term, and found the men tended to crank up genes that stunt hair growth.

The work was published in PLOS One.

Hair growth isn’t a constant dribble from the follicle – it’s a cycle. The anagen phase, or growth phase, can last between two and six years. The hair then enters the catagen or transitional phase, a two-week period where the follicle shrinks and cuts the hair strand off from its blood supply.

Then during the telogen or resting phase, the follicle remains dormant for a few weeks to a few months. Eventually, the follicle will “wake”, snap the old hair off at its base (which we know as shedding) and a new hair is pushed out.

Recent work on mice that spent time in Earth orbit showed the number of hair follicles in anagen decreased, and that prolonged spaceflight might kick off skin atrophy and upset the hair follicle’s cycle. Could this be the case in people too?

Part of an experiment nicknamed “HAIR”, which the Japanese Aerospace Exploration Agency (JAXA) has run since 2009, Terada and colleagues looked at gene expression in hair follicles of 10 astronauts who spent six months or more on the space station.

The subjects plucked five hairs, with follicle attached, from their head at six intervals: twice before heading into space, twice while in space and twice again once they returned to Earth.

Then the researchers examined RNA in follicle cells – signs that various genes are turned on or off at time of plucking.

The results between astronauts, not surprisingly, varied, but they did find some trends.

Four genes that decrease hair growth ramped up while in space – but only for the men, and they dropped to normal levels once they returned to Earth. The two female astronauts’ hair-growth genes remained stable throughout spaceflight.

So why does spaceflight tinker with gene expression in men – and why are women seemingly immune?

It’s hard to say, the researchers write, because there is no single gene that controls hair growth. The differences could be due to diet, lifestyle or psychological state, all of which affect hair growth on Earth and are disrupted in space.

Having access to metabolic data might allow the team to correlate hair growth with physiology, but they didn’t have that information. They also admit the small sample size is an issue, but very few people have set foot on the space station, let alone lived there for half a year or longer.

But as more astronauts are shot up into orbit, that number will increase. And in good news for male astronauts: less time in the barber’s chair for you.

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